Physical inactivity and overweight/obesity are important risk factors for a number of cancers, including breast and colon. Physical activity levels among U.S. adults are less than optimal and there is a growing epidemic of obesity. There is increasing evidence that certain aspects of the neighborhood built environment influence physical activity and that factors such as greater urban sprawl are related to overweight. Studies to-date have important limitations, including infrequent use of smaller scale objective environmental measures, scant research using both objective and perceived environmental measures, and limited evidence for older adults. For this two-year exploratory R21 study, we have assembled an experienced transdisciplinary team of researchers from public health, urban planning and geography to develop sound measures of the built environment for older women in the Nurses Health Study (NHS) and to assess the effects of these factors on physical activity, BMI, overweight, and obesity. Our specific aims are: 1) develop household-level objective measures of the built environment for approximately 30,000 NHS participants in three states and examine cross-sectional associations with physical activity and weight-related outcomes; 2) measure perceptions of neighborhood environment and physical activity in a sub-sample of 3800 women and assess associations between perceived and objective environmental measures and key outcomes; and 3) pilot test the use of high-resolution orthophotographs to develop several micro-scale measures of the built environment. We will obtain publicly and commercially available geographic information systems (GIS) data in order to create household-level measures of residential density, land use mix, and street connectivity for NHS participants in MA, PA, and CA with geocoded home addresses. We will survey women with the Neighborhood Environment Walkability Scale (NEWS) and the Physical Activity Scale for the Elderly (PASE). In a small sample in MA, we will use orthophotographs to create several micro-scale measures of the built environment (e.g., amenities for walking). To test for associations we will use multivariable modeling techniques that control for potential individual and environmental confounders. A key goal of this study is the development of methods that can be used in future prospective studies that may help elucidate causal pathways between the built environment and physical activity and obesity. Also, we anticipate using the findings from this study to design more effective physical activity interventions for older women that incorporate environmental strategies. Relevance: This study may yield new insights into how characteristics of neighborhood environments influence older women's participation in regular physical activity and information as to how these characteristics may be related to the risk of overweight and obesity. We plan to use this study's results to develop more effective initiatives to promote physical activity among older women that take into consideration neighborhood characteristics and resources. Ultimately, this study's findings may help to decrease the risk of several cancers related to lack of physical activity -- both among older adults and younger populations. [unreadable] [unreadable] [unreadable]